Electro-mechanical actuator

ABSTRACT

An electro-mechanical actuator including a plurality of motors for driving an output shaft. The actuator may be incorporated into a window lift mechanism, such as a mechanism including a dual rack and pinion assembly. According to another aspect of the invention there is provided a variety of anti-back-drive mechanisms, e.g. clutches. A clutch according to one embodiment includes locking pawls that resist back-drive. In another embodiment, locking cams rotate relative to a carrier to resist back-drive. An actuator consistent with the invention may incorporate an impact mechanism including a flexible carrier. The carrier flexes to prevent impact forces at an output gear train from coupling to an input gear train.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing dates of U.S.Provisional Application Nos. 60/176,847 and 60/178,593 filed Jan. 19,2000 and Jan. 28, 2000, respectively, the teachings of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to an electro-mechanicalactuator, and, in a particular embodiment, to an actuator for raisingand lowering a window such as an automobile window.

BACKGROUND OF THE INVENTION

Electro-mechanical actuators are commonly used for a wide variety ofapplications. In an automotive setting, for example, actuators may beused for raising and lowering windows, for opening and closing sunroofs,controlling windshield wipers, etc. In a power window application, forexample, an actuator may be located in each door assembly having anoperable window, and usually includes an electric motor of some sort anda drive mechanism for raising and lowering the window, or in the case ofthe sunroof, for example, for opening and closing, or otherwise movingthe sunroof.

Power windows, sunroofs, etc. are conventionally driven by a singlemotor, which may be gear driven or of a worm gear configuration,connected to a mechanism for raising and lowering the window, operatedby means of a switch control. Such an actuator is disclosed, forexample, in U.S. Pat. No. 5,801,501, wherein a single motor drives aworm gear drivably connected to mechanism for lifting the window ormoving the sunroof. This configuration transmits all torque from asingle motor. The higher friction and lower efficiency worm driveresults in lower overall system efficiency, and greater electrical powerrequirements to achieve sufficient power output.

Such single motors are often larger in size than may be desirable froman overall design standpoint and may require a comparatively largeamount of electric current in order to function smoothly, efficiently,and responsively. U.S. Pat. No. 5,787,644, for example, discloses apower window system with the drive motor located within the body ratherthan within the door of the vehicle due to the size of the motor.Although this alleviates, in part, the design concerns, the problemsassociated with engine size and power requirements remain.

Utilizing a smaller motor, however, sacrifices motor power, speed andefficiency. Moreover, if the motor fails, the window, sunroof, wiper,etc., as the case may be, is rendered inoperable, whether in open orclosed position. Not only are such failures common, they occur withoutany prior notice. U.S. Pat. No. 5,024,022 addressed these issues byproviding an automobile window opening and closing device which has amanually operated mechanism and a power-operated mechanism incombination. This configuration, however, represents a step backwardsfrom the full power window or sunroof features desired in today'sautomobiles.

An application that uses two motors is found in a device forautomatically adjusting a rearview mirror, U.S. Pat. No. 4,815,837.There, each electric motor operates a separate drive mechanism forperforming a distinct adjustment of the angles of the mirror. U.S. Pat.No. 5,346,045 discloses an electrically powered linear actuator forsupporting and moving the cabin of a fight simulator, including twolarge motors capable of moving and supporting the substantial weight ofthe simulator, each having a pinion engaging a chain or gear traincoupling, which drives a pulley secured to the end of a screw threadeddrive shaft driving a traveling member.

There is therefore a need in the art for an efficient and cost-effectiveactuator to design that overcomes the deficiencies of the prior art.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided an actuatorincluding: an output shaft for driving a window lift mechanism; anoutput gear coupled to the output shaft; and a plurality of motorscoupled to the output gear for driving the output gear and the outputshaft. A window lift mechanism according to another aspect of theinvention includes: a dual rack assembly having first and second opposedracks; first and second pinions in meshing engagement with the first andsecond racks, respectively; and an actuator assembly comprising aplurality of motors for driving the first and second pinions along thefirst and second racks.

According to another aspect of the invention there is provided a varietyof clutches for preventing back-drive in an actuator. One clutchaccording to the invention includes an output gear and an input gearconcentric with the output gear. The output gear has at least one notchat a perimeter thereof for receiving an associated tab on interiorsurface of the input gear. The interior surface of the input gearfurther includes a locking pawl notch. The clutch further includes firstand second locking pawls. The locking pawls are joined by a spring anddisposed at opposite ends of the locking pawl notch adjacent theperimeter of the output gear. Upon rotation of the input gear, the tabengages the at least one notch to rotate the output gear in a firstdirection. Upon rotation of the output gear in a second directionopposite to the first direction, the locking pawls engage the outputgear to resist rotation of the output gear.

Another clutch consistent with the invention includes: a carrierdisposed on an output shaft; and a plurality of cams. Each of the camsis pivotally coupled to the carrier and has an end positioned adjacent acam engaging surface. Upon application of a rotational force to theoutput shaft in a first direction, the cams pivot relative to thecarrier to allow rotation of the output shaft. Upon application of arotational force to the output shaft in a back-drive direction, the camspivot relative to the carrier to engage the cam-engaging surface toresist rotation of the output shaft.

According to another aspect of the invention there is provided anactuator including an impact mechanism. The actuator includes: aflexible carrier assembly; a gear train coupled to the flexible carrierassembly, the gear train including a worm gear coupled to a worm wheel;an input gear train including a first spur gear in meshing engagementwith the worm wheel; an output gear train including a second spur gearin meshing engagement with the worm gear; and at least one motor fordriving the input gear train. Upon application of a linear force to anoutput gear of the output gear train, the flexible carrier assemblyflexes to substantially prevent the linear force from coupling to theinput gear train.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, together with otherobjects, features and advantages, reference should be made to thefollowing detailed description which should be read in conjunction withthe following figures wherein like numerals represent like parts:

FIG. 1 is a perspective view an exemplary actuator powered by two motorsand gear trains coupled to a drive gear consistent with the presentinvention;

FIG. 2 is a plan view of the exemplary actuator illustrated in FIG. 1;

FIG. 3 is a front view of the exemplary actuator illustrated in FIG. 1;

FIG. 4 is a side view of the exemplary actuator illustrated in FIG. 1;

FIG. 5 illustrates another exemplary embodiment of an actuatorconsistent with the invention wherein a planetary gear system is drivenby separate worm and spur gear arrangements;

FIG. 6 is a partial sectional view of the embodiment illustrated in FIG.5;

FIG. 7 illustrates another exemplary embodiment of an actuatorconsistent with the invention wherein a planetary gear set is driventhrough two separate worm gear sets;

FIG. 8 illustrates another exemplary embodiment of an actuatorconsistent with the invention wherein multiple motors drive a singleface gear;

FIG. 9 is a side view of the exemplary embodiment illustrated in FIG. 8;

FIG. 10 illustrates an exemplary actuator consistent with the inventionmounted for driving a window in a dual rack system;

FIG. 11 diagrammatically illustrates a side view of the arrangementillustrated in FIG. 10;

FIG. 12 illustrates a sectional view taken along lines 12—12 in FIG. 10;

FIG. 13 illustrates an alternative actuator configuration for use inconnection with a dual rack system as shown in FIG. 10;

FIG. 14 diagrammatically illustrates an arrangement including threeseparate motors for driving an output shaft connected to a face gear;

FIG. 15 is a circuit diagram illustrating electrical connections for amultiple motor assembly as shown in FIG. 14 for example;

FIG. 16 illustrates an exemplary bi-directional clutch anti-back drivemechanism consistent with the invention;

FIG. 17 is a sectional view of the mechanism illustrated in FIG. 16;

FIG. 18 diagrammatically illustrates a solenoid back drive mechanism inconnection with an actuator consistent with the invention;

FIG. 19 illustrates a solenoid anti-back drive mechanism as shown inFIG. 18 wherein a solenoid plunger is engaged with an intermediate gearfor preventing back drive;

FIG. 20 illustrates an exemplary intermediate gear including pockets forreceiving a solenoid plunger in a solenoid anti-back drive mechanism asshown, for example, in FIGS. 18 and 19;

FIG. 21 illustrates another exemplary anti-back drive mechanismconsistent with the invention;

FIG. 22 illustrates a bottom view of the mechanism illustrated in FIG.21;

FIG. 23 illustrates an exemplary mounting arrangement for an anti-backdrive mechanism as shown in FIGS. 21 and 22;

FIG. 24 illustrates another exemplary clutch mechanism consistent withthe invention;

FIG. 25 is an exploded view of the exemplary clutch mechanismillustrated in FIG. 24;

FIG. 26 diagrammatically illustrates an exemplary impact mechanismuseful in connection with an actuator consistent with the invention; and

FIG. 27 is a partial side view of the impact mechanism illustrated inFIG. 26.

DETAILED DESCRIPTION

Referring to FIGS. 1 through 4, an exemplary actuator 1 consistent withthe invention is illustrated. As shown, the actuator 1 includes twoelectric motors 2 and 3. A control circuit 40 controls energization ofthe motors. The control circuit may include, for example, a simpleswitch, or more complex arrangement providing pinch resistance, expressopen/close, etc.

Motor 2 has a first drive pinion 4 disposed about its output shaft 5which engages worm wheel 6 attached to worm gear 7. The worm gear 7engages spur gear 8 for driving an actuator output shaft 10. The outputshaft is provided in driving relationship to a mechanism to be driven,e.g. a window lift mechanism 30. The window lift mechanism may include,for example, a conventional scissor lift, a cable and pulley mechanism,etc. The present invention is not, however, limited to window liftapplications. In fact, an actuator consistent with the invention may beprovided to drive a wide variety of mechanisms for achieving theattendant advantages.

Motor 3 drives a gear train including individual gears 11 a-d. Piniongear 11 a is disposed about the motor shaft 12, the end portion of whichalso serves to align high efficiency gear 11 d and drive gear 13attached to high efficiency gear 11 d. The drive gear 13 engages asecond high efficiency gear face gear 14, which drivably engages outputspur gear 8 for driving the output shaft 10. Gears 11 b and 11 c aresecured by gear shaft 15.

When both the electric motors 2 and 3 are energized, worm gear 7 andhigh efficiency gear 14 both independently drive spur gear 8 and shaft10 causing the window, sunroof, etc. to be opened or closed. Since thetwo motors 2 and 3 do not share the same gear trains, they can becontrolled on different circuits and may produce variable speed andtorque rotary output or other power distribution arrangements. Forexample, the motors may be configured so that the inherent torque rippleof the motors is out of phase with one another. This may reduce orcancel actuator vibration and hum inherent in a single motor. There isan inherent resolution of output rotational speed proportional with thenumber of motors and gear train sets. Meaningful variations can beachieved by combining multiple motors on either parallel drive trains orconnecting the motors in series, along with any combination of clutchdevices.

In addition, multiple motors on a common drive train provide a softfailure mode in the event that one motor fails. The remaining motorswill provide basic function at a reduced performance level until servicecan be performed. When combined with simple electronic control circuitrynumerous torque and speed outputs can be achieved without introducingadvanced velocity control electronics such as Pulse Width Modulation orproportional voltage adjustment. For example, the actuator can operateon motor 2 (“A”) only, motor 3 (“B”) only, “AB”, “A with B reversed”,etc.

The application of a worm gear 7 and worm wheel 6, driven only by motor2 in conjunction with a high-efficiency parallel drive train driven bymotor 3 provides anti-back drive and passive braking/clutching features.Back drive of the output shaft 10 is inherently limited by the worm gearwhile preserving the higher acceleration and efficient torque transferof the motor 3. The worm gear 7 coupled to the motor 2 thus acts like aclutch in the system 1.

If the high efficiency drive train powered by motor 3 is designed suchthat its output rotational speed is greater than the motor and drivetrain, the worm gear will inherently limit the actuator's overall outputrotational speed. At speeds above this point the apparent motion of thecommon output begins to accelerate the worm gear train, which acts likea brake. In addition, the inherently high friction of the worm gear when“reversed” provides a high drag load to the system multiplied by thegear ratio of the worm gear consuming any additional power generated bythe high efficiency drive train. This governs the system to an outputspeed closely approximating the no load speed of the worm gear train ofthe system.

A variety of multiple motor configurations consistent with the inventionare possible. FIGS. 5 and 6, for example, illustrate an exemplaryactuator consistent with the invention wherein the output shaft isdriven through a planetary gear system 500. In the illustratedembodiment, the planetary gear set includes a stationery sun gear 502.Ring gear 504 rotates around the sun gear with planet gears 506 in amanner well known to those skilled in the art. Consistent with theinvention, the ring gear is driven by a worm gear drive set 508 and aspur gear drive set 510. A first motor 512 drives the worm gear 514 anda second motor 516 drives a spur gear 518, potentially throughintermediate gears 520, 522, respectively. As in the embodimentillustrated in FIGS. 1-4, the worm gear inherently provides anti-backdrive characteristics.

Coarse pitched teeth on the outer ring 504 are preferable for achievingappropriate efficiency and back drive characteristics. Those skilled inthe art will recognize that, as an alternative to the illustratedembodiment, the output shaft 530 could be in fixed relation to rotatablesun gear with the ring gear in a fixed position.

An alternative planetary gear arrangement is illustrated in FIG. 7. Theembodiment illustrated in FIG. 7 is substantially similar to that shownin FIGS. 5 and 6 with the main exception being the inclusion of two wormgear drive sets instead of a worm gear drive set and a spur gear driveset. As shown, the ring gear 504 and planetary gears 506 are drivenaround a fixed sun gear 502 by a first worm gear 700 driven by a firstmotor 702 and separately by a second worm gear 704 driven by a secondmotor 706. Again, it will be recognized by those skilled in the art theeither the ring gear affixed to sun gear or a carrier for planetarygears may be coupled to the output shaft for driving the shaft.

FIGS. 8 and 9 illustrate another alternative embodiment of an actuatorconsistent with the invention wherein first and second motors 800 and802 separately drive a face gear 804, which may drive a spur gear setincluding gears 806 and 808 for driving an output shaft 810 connected togear 808. As shown in FIG. 9, the face gear may be a compound gearincluding a pinion 812 for driving compound gear 806, which includes apinion 814 for driving gear 808. Pinions 816 and 818 on motors 800 and802 respectively engage the face gear for driving the same.

FIGS. 10-12 illustrate an exemplary actuator consistent with theinvention configured in a dual rack arrangement for driving a window ina power window system. As shown in FIG. 10 an actuator 1002 consistentwith the invention may be configured for driving first and secondpinions 1004 and 1006 along opposed racks 1001, 1003 of a known dualrack 1000. As is known, the window glass 1008 (FIG. 11) may be securelycoupled to the pinions or the actuator assembly, and the rack may beheld stationery within a door. As the actuator drives the pinions, thepinion, actuator and glass assembly translates along the rack foropening and closing the window depending on the direction of rotation ofthe pinions.

As shown in cross-sectional view in FIG. 12, an exemplary actuator 1002may include a first motor 1200 driving a worm gear 1202 and a secondmotor 1204 driving a spur gear set 1206 in a manner consistent with theinvention, as described for example in connection with FIGS. 1-4. Theworm gear and spur gear sets may drive a gear 1208, which in turn drivesoutput gear 1210 having a driving shaft 1212 connected for driving thefirst pinion 1006. The first pinion may be in meshing engagement withsecond pinion 1004, which is rotatable on a carrier axle 1214. Theactuator assembly may include first and second arms 1216 and 1218respectively having portions that extend into grooves 1220, 1222,respectively. When the motors are energized, the actuator drives thepinions to cause translation of the actuator, pinion and glass assemblyalong the dual racks with the actuator sliding along the grooves 1220,1222.

Those skilled in the art will recognize that a variety of configurationsof an actuator consistent with the invention may be incorporated into adual rack system for an automotive window lift application. For example,FIG. 13 illustrates an alternative embodiment including two separatemotors 1300 and 1302, which separately drive first and second pinions1304 and 1306 through associated worm gear drives 1308 and 1310,respectively. Again, the actuator housing 1312 would be attached to theautomotive glass so that the glass would move up and down relative tothe dual racks 1314 to raise and lower the window with actuation of themotors 1300 and 1302.

Turning now to FIG. 14, there is illustrated a face gear 1400 with anoutput shaft 1410 affixed thereto for driving a mechanism consistentwith the invention. As shown, the face gear is driven by first, secondand third motors 1412, 1414 and 1416 through associated pinions 1418,1420 and 1422, respectively. FIG. 14 illustrates the advantagesassociated with using multiple motors for driving a common output shaft.It is to be understood, however, that multiple motors could be arrangedin any way to drive the common output shaft, which could be connected toa face gear, a planetary gear set, etc.

As shown in FIG. 15, an electronic control module 1500 may be providedfor selectively energizing the respective motors. Based on operatorinput, the electronic control module or other switch arrangement can beprovided to control how many motors are energized and in whichdirections. Depending on the number of motors provided in an actuatorconsistent with the invention, the load and speed for driving the motorsmay vary.

For example, in a power window application an “express up” condition maybe desired for moving the window to a closed position at a rapid pace.With reference to the embodiment illustrated in FIG. 14, in an “expressup” a condition, the electronic control module may energize all threemotors simultaneously based on an operator input to achieve thenecessary torque and speed for driving a window at a high rate. Inaddition, a sensor or sensors may be provided to sense when the windowis at a nearly closed position to reduce the driven speed of the windowwhen it is nearly closed by, for example, de-energizing one or more ofthe motors. Also, the sensors may be incorporated into the assembly foridentifying when an object is in the path of the window to preventcrushing of the object between the window and the window frame. When anobject is present, the electronic control module may, for example,disable all the motors to provide “pinch resistance.” A rain sensorcould also be provided for causing energization of the actuators toclose the window when it is raining.

As noted herein, a multiple motor actuator arrangement may also providesignificant utility in connection with window wiper systems and sunroof.For example, the multiple motors can be configured for driving wipers atdifferent speeds. The electronic control module 1500 may energize allmotors in the system to drive the wipers at a high rate of speed, andmay energize somewhat less than all of the motors to drive the wipers ata lower speed. In addition, an actuator according to the invention canbe provided to allow a predetermined amount of back drive so that anelectronic control module 1500 may back drive a wiper blade into an athome position after the wipers are de-energized.

Anti-backdrive in an actuator consistent with the invention may beaccomplished using a worm gear set or solenoid device, as discussedabove, or other clutch-type mechanisms. FIGS. 16 and 17, illustrate anexemplary bi-directional clutch anti-back drive mechanism consistentwith the invention. As shown, first and second motors 1600 and 1602drive an input gear 1604, e.g. a face gear, through pinions 1606 and1608. It will be understood by those skilled in the art that any geartrain may be provided between the motors and the pinions 1606, 1608 fordriving the face gear and that the face gear could be substituted with aspur configuration, worm gear, etc.

In the illustrated embodiment, the interior surface of the face gearincludes first and second spaced tabs 1610 and 1612 and a notch 1614.Locking pawls 1616, 1618 are disposed at opposite ends of the notch 1614and connected by a spring 1620. With rotation of the face gear by themotors, the edge 1622 of the notch engages the locking pawl 1616 causingrotation of the locking pawls with the face gear. Tabs 1610 and 1612engage edge surfaces of notches 1611, 1613, respectively, on an outputgear 1624 to which the output shaft 1626 is secured. Back drive isprevented in the illustrated mechanism since rotation of the outputshaft causes engagement of the output gear with the locking pawls toprevent rotation of the output gear.

Turning now to FIGS. 18-20, there is shown an exemplary solenoidanti-back drive device consistent with the invention. In the illustratedembodiment, multiple motors 1800, 1802 are attached for driving anintermediate gear consisting of a face gear 1804 and a pinion 1806combination. Between the motors and the face gear is a system of highefficiency spur gears that are back drivable.

A solenoid 1808 shares the same power supply as the motors. In anun-energized state, the solenoid plunger 1810 is extended, locking intothe side of the intermediate gear 1804, as shown for example in FIG. 19.When the motors are energized, the solenoid is also energized, and thesolenoid plunger retracts to unlock the system, as shown in FIG. 18, forexample. The pinion 1806 may be configured to meshingly engage a spuroutput gear 1812 to which an output shaft 1814 is attached. Asillustrated more particularly in FIGS. 19 and 20, the solenoid may beprovided with a load spring 1900, and the intermediate gear 1804 may beprovided with a plurality of equally spaced pockets 1902 for receivingthe solenoid plunger in an anti-back drive position. Advantageously, dueto the gear ratio between the intermediate gear, the output gear and thewindow regulator itself, the rotation between pockets 1902 results invery little motion of the window if the solenoid plunger needs to find ahome in a pocket 1902.

Another exemplary anti-back drive clutch mechanism is illustrated inFIGS. 21 through 23. As shown in FIG. 21, for example, the mechanism2100, may include a face gear 2102 with a central shaft 2104. A mountingplate 2106 may be provided at the end of the shaft 2104 to provide amounting position for a plurality of cams 2108. The cams are pivotallyattached to the plate 2106 by pins 2300, as shown for example in FIG.23.

A plurality of motors, for example, motors 2110 and 2112 may be providedfor driving the face gear 2102. With rotation of the face gear by themotors, the cams 2108 rotate about the pins 2300 and ride along theinterior surface 2114 of the face gear. However, when a back drive isapplied to the system, the back drive force rotates the shaft 2104through, for example, an associated gear train 2115 to which the outputshaft 2116 is coupled. Rotation of the plate causes the cams to pivotabout the pins for pressingly engaging the interior surface 2114 of theface gear. With the pins rotated in this manner, engagement of the pinsagainst the interior surface of the face gear prevents further rotationof the shaft 2104, thereby preventing back drive in the system.

FIG. 22 illustrates a bottom view of the system illustrated in FIG. 21,and more particularly shows an exemplary gear train for driving theoutput shaft 2116. In particular, the shaft 2104 may have a pinionaffixed to an opposite end thereof for driving the spur gear set 2114.FIG. 23 illustrates an alternative mounting arrangement for the clutchillustrated in FIG. 21 wherein the housing 2302 is provided forenclosing the motors.

FIGS. 24 and 25 illustrate yet another alternative anti-back driveclutch mechanism 2400. In the illustrated embodiment, the mechanism 2400includes a carrier 2402, which is preferably driven by an actuatorassembly consistent with the invention. A plurality of cams 2404 arepivotally attached to the carrier by pins 2406. Bias springs 2408 aredisposed between tabs on the carrier and the cams. A hub 2410 isdisposed over a center axis 2412 of the carrier to define a range ofmotion for the cams 2404.

Rotation of the carrier by an actuator causes the cams 2404 to pivotabout the pins 2406 and to ride along the interior surface 2416 of amounting opening 2414 for the mechanism. When a back drive force isapplied to the shaft 2412, however, the cams rotate about the pins 2406to pressingly engage the interior surface 2416 and thereby resistrotation of the shaft 2412 to provide an anti-back drive.

FIGS. 26 and 27 illustrate an exemplary impact mechanism consistent withthe invention. As shown a motor 2600, for example, one of the motors ina multiple motor configuration consistent with the invention drives aworm gear 2602 mounted on a worm wheel 2604 (i.e. a spur gear) through apinion 2606. The worm gear meshingly engages a spur gear 2608, whichincludes a pinion 2610 for driving an output gear 2612 to which anoutput shaft 2614 is attached.

Those skilled in the art will recognize that a variety of gear trainsmay be incorporated into the illustrated design. Advantageously,however, the worm gear and worm wheel are mounted on the impactmechanism 2616, which includes a carrier 2618 having first 2702 andsecond 2706 flexible arms. As shown in FIG. 27, a first end 2700 of theworm gear and worm wheel assembly is rotatably mounted on the first arm2702 of the carrier assembly 2618 and second end 2704 of the worm gearand worm wheel assembly is mounted on the second arm 2706 of the carrierassembly. The arms of the carrier assembly are configured to flex up anddown as indicated by arrows 2620 with a known spring rate. If an impactis applied to the output shaft 2614, for example, if an automobilewindow driven by the mechanism is unexpectedly impeded or arrestedduring closing, then the impact imparted to the output gear shaft istransmitted through gears 2612, 2608 to the worm gear 2602 and isabsorbed by flexure of the carrier 2616. Advantageously, therefore, theimpact is not transmitted to the motor causing damage thereto.

There is thus provided, according to one aspect of the invention, anactuator that employs two or more motors connected to a geared drivetrain(s) to produce variable speed and torque rotary output. Employingmultiple smaller motors to provide an equivalent amount of power via agear train or gear trains provides significant advantages over using alarger single motor. An actuator design using multiple small motors canbe thinner and permit assembly in a wider variety of orientations andpackage shapes. Multiple motors do not need to share same gear train ormay be located on parallel gear trains to provide novel powerdistribution arrangements. Multiple motors can also be of differentsizes, varieties, or have different load characteristics connectedthrough a common output shaft. Additionally, each separate motor can becontrolled on a different circuit to provide novel and unique torque vs.speed output.

Multiple motors can be selected to have an extended brush/rotor lifecompared to a single equivalently powered large motor. The multiplemotors can be set in a novel way so that the inherent torque ripple ofthe motors are out of phase with one another. The overall output torqueis smoother. This can reduce or cancel actuator vibration and huminherent in a single motor. Multiple motors on a common drive trainprovide a soft failure mode in the event that one motor fails. Theremaining motors will provide basic function at a reduced performancelevel until service can be performed. This degraded operation mode canbe diagnosed remotely, allowing the computer to alert the driver of aservice/maintenance problem and even cause a change in the controlscheme. This enhances reliability of the actuator compared to a singlemotor design where failure of the motor is critical.

A multi-motor actuator has unique benefits that can be advantageous in awindow lift application. When combined with simple electronic controlcircuitry numerous torque and speed outputs can be achieved withoutintroducing advanced velocity control electronics such as Pulse WidthModulation or proportional voltage adjustment. For example, the actuatorcan operate on motor “A” only, “B” only, “AB”, “A with B reversed” etc.There is an inherent resolution of output rotational speed proportionalwith the number of motors and gear train sets. Meaningful variations canbe achieved by combining multiple motors on either parallel drive trainsor connecting the motors in series, along with any combination of clutchdevices.

An impact mechanism for absorbing rotational impact on an actuatoroutput shaft and preventing damage associated therewith is alsoprovided. According to another aspect of the invention there areprovided anti-back drive features that prevent undesired motion in adriven system. For example, in a window lift application, actuatorprevents the window from being lowered either inadvertently or byexternal means. It is frequently important in window regulator systemsto prevent movement of the output shaft in the power off condition tohold the window in any fixed position indefinitely. This is importantfor at least two reasons: 1) to resist drifting due to vibration of thewindows mass and 2) to resist forced entry into the vehicle by slidingor otherwise moving the window.

The embodiments that have been described herein, however, are but someof the several which utilize this invention and are set forth here byway of illustration but not of limitation. It is obvious that many otherembodiments, which will be readily apparent to those skilled in the art,may be made without departing materially from the spirit and scope ofthe invention as defined in the appended claims.

1. An actuator for a window lift mechanism, said actuator comprising: anoutput shaft for driving said mechanism; an output gear coupled to saidoutput shaft; a plurality of motors coupled to said output gear forsimultaneously driving said output gear and said output shaft, whereinsaid plurality of motors comprises a first motor having a first torqueripple characteristic and a second motor having a second torque ripplecharacteristic, wherein said first torque ripple characteristic is atleast partially out of phase with said second torque ripplecharacteristic to reduce vibration imparted to said actuator by saidplurality of motors.
 2. An actuator according, to claim 1, wherein eachof said motors is coupled to said output gear by an associated geartrain.
 3. An actuator according to claim 2, wherein a first one of saidgear trains comprises a worm gear in meshing engagement with said outputgear, said worm gear resisting back-drive of said output shaft.
 4. Anactuator according to claim 1, wherein said output gear comprises a sungear of a planetary gear system, and wherein said motors are coupled tosaid sun gear through a ring gear and planet gears of said planetarygear system.
 5. An actuator according to claim 4, wherein each of saidmotors is coupled to said gear by an associated gear train.
 6. Anactuator according to claim 5, wherein a first one of said gear trainscomprises a worm gear in meshing engagement with said sun gear, saidworm gear resisting back-drive of said output shaft.